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PREFACE BIOLOGY 



IN the following Introduction to the study of the Comparative 

 Anatomy of Animals, I have necessarily been guided by the 

 requirements of the elementary examinations at the leading 

 universities of Great Britain. 



Having found by experience that beginners find great 

 difficulty in apprehending the full meaning of the cell- theory 

 at the commencement of their studies, I have departed from 

 the course usually pursued in lectures and practical instruction, 

 and instead of beginning with the study of cells, I have taken 

 the common frog as a type of animal organisation. The general 

 anatomy of the frog is first described in some detail; the 

 microscopic structure of its organs and tissues is next explained, 

 and then the cell-theory and the phenomena of the cell-division 

 are dealt with. In this way I have attempted to lead the 

 student gradually from familiar to new and unfamiliar concep- 

 tions. 



I have attempted, as far as possible, to verify by personal 

 observation the statements of fact contained in this book, but 

 want of time and opportunity has prevented me from repeating 

 the long and laborious researches of many investigators on 

 such subjects as the reproduction of the Protozoa. Where 

 personal observation has been wanting I have tried to give 

 an adequate account of the best and most recent researches 

 on the subject. In certain cases, however, I have preferred 

 the results of older to those of more recent observers. For 

 example, I have adhered to Maupas' account of the phenomena 

 of conjugation in the Ciliata, because in my judgment the 

 results of the latest researches on this matter require inde- 

 pendent confirmation before they can be held to overthrow 

 the results of such careful and consistent work as that of 

 Maupas. Since this book is in part a record of my own 

 observations and not wholly a compilation, I have in several 

 cases departed ' from the accepted accounts of certain 

 phenomena. Thus the description of the truncus arteriosus 

 ix 



218 



